Proposed resolution (approved by CWG 2023-11-11):

Change the grammar in 13.7.2.3 [temp.deduct.guide] paragraph 1 as follows:

deduction-guide:
   explicit-specifieropt template-name ( parameter-declaration-clause ) requires-clauseopt -> simple-template-id ;

[Accepted as a DR at the March, 2024 meeting.]

The grammar for deduction-guide does not, but should, allow a trailing requires-clause:

deduction-guide:
   explicit-specifieropt template-name ( parameter-declaration-clause ) -> simple-template-id ;